I have tried a number of times to make VLC Media player the default for MP3 and MP4. I open a file and tick the "Always open with" checkbox, but they still open with iTunes and QuickTime by default respectively. Does anyone know how to fix this?
Try these 2 solution maybe it solve your problem:
1- use "Default Apps" for change every default application.
2- From the Finder, select a MP-4 file, open the Info panel (